An integrated circuit (IC) is formed by creating one or more devices (e.g., circuit components) on a semiconductor substrate. Each device is separated from the other devices using an isolation feature such as a shallow trench isolation (STI) structure. Current STI structures often include silicon oxide such as high density plasma chemical vapor deposition (HDPCVD) silicon oxide or silicon oxide by a high aspect ratio process (HARP silicon oxide). However, high stress may be induced by those STI structures, such as a compressive stress in the active region of the silicon substrate after an annealing process. The compressive stress can degrade the electron mobility of the silicon substrate in the active regions. In addition, the saturation current in an n-metal-oxide-silicon field-effect-transistor (nMOSFET) can be decreased thereby. Furthermore, the high stress may cause a leakage current that affects the performance of the resulting device.